Copolyester-carbonates are well known thermoplastic materials which, due to their many excellent properties, find use in many commercial and industrial applications. These copolyester-carbonates exhibit, for example, excellent properties of toughness, flexibility, impact resistance, and high heat distortion temperatures. The copolyester-carbonates, as described in U.S. Pat. No. 3,169,121, are generally prepared by the reaction of a dihydric phenol, a carbonate precursor, and a difunctional carboxylic acid. However, due to their relatively high melt viscosities the copolyester-carbonates are generally difficult to process, even at high temperatures. It would thus be very advantageous if a copolyester-carbonate could be provided which retained all of the other advantageous properties of copolyester-carbonates and was also easier to process, i.e., exhibited lower melt viscosities.
It is, therefore, an object of this invention to provide copolyester-carbonate resins which exhibit improved processability and which simultaneously retain all of the other advantageous properties of copolyester-carbonates.